CN111155036B

CN111155036B - Sliding member for variable oil pump for vehicle and method for manufacturing same

Info

Publication number: CN111155036B
Application number: CN201911081673.3A
Authority: CN
Inventors: 金鹤洙
Original assignee: Hyundai Motor Co; Kia Motors Corp
Current assignee: Hyundai Motor Co; Kia Corp
Priority date: 2018-11-07
Filing date: 2019-11-07
Publication date: 2023-01-24
Anticipated expiration: 2039-11-07
Also published as: US11668298B2; CN111155036A; US20200141404A1; DE102019217238A1

Abstract

The present invention provides a method for manufacturing a slider of a variable oil pump for a vehicle, the method including: a pre-alloyed powder including, in percent (%) by weight of the entire components, 0.45 to 0.55% of carbon (C), 2.8 to 3.2% of chromium (Cr), 0.45 to 0.55% of molybdenum (Mo), 0.35 to 0.5% of manganese (Mn), 0.1 to 0.25% of sulfur (S), and the balance iron (Fe) and inevitable impurities is used to prepare a compact of a sliding member of a variable oil pump; preparing a sintered body by sintering the molded body; slowly cooling the sintered body to enable the temperature of the sintered body to reach a first temperature range; and rapidly cooling the sintered body when the first temperature range is reached.

Description

Sliding member for variable oil pump for vehicle and method for manufacturing same

Technical Field

The present disclosure relates to an oil pump of a vehicle.

Background

The oil pressure required by the engine varies according to Revolutions Per Minute (RPM). Typically, the oil pressure is parabolic in shape. However, existing oil pumps provide a straight line shape of oil pressure, which results in a fuel efficiency loss of about 2%.

Recently, in order to improve fuel efficiency, a variable oil pump that can control the amount of oil flowing into the pump is increasingly employed. The variable oil pump is a device for generating oil pressure by a vane (vane) or a pendulum (pendulum) which is made of a high chromium (Cr) based material and is in contact with an inner diameter of a sliding member. The variable oil pump is subjected to a steam treatment or a nitrification treatment for wear resistance of the sliding member, but the steam layer/nitrification layer peels off during the line fault evaluation, and thus a method for coping with severe conditions is required.

Disclosure of Invention

Embodiments of the present disclosure may provide a sliding member of a variable oil pump for a vehicle, which is capable of improving dimensional accuracy using pre-alloyed powder and an improved sinter hardening method. A method of manufacturing a slider is also disclosed.

Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

According to an aspect of the present disclosure, a method of manufacturing a slider of a variable oil pump for a vehicle includes: a pre-alloyed powder including, in percent (%) by weight of the entire components, 0.45 to 0.55% of carbon (C), 2.8 to 3.2% of chromium (Cr), 0.45 to 0.55% of molybdenum (Mo), 0.35 to 0.5% of manganese (Mn), 0.1 to 0.25% of sulfur (S), and the balance iron (Fe) and inevitable impurities is used to prepare a compact of a sliding member of a variable oil pump; preparing a sintered body by sintering the molded body; slowly cooling the sintered body to enable the temperature of the sintered body to reach a first temperature range; and rapidly cooling the sintered body when the first temperature range is reached.

Slowly cooling the sintered body to bring the temperature of the sintered body to the first temperature range may include: the sintered body is furnace cooled to a temperature in the range of 830 to 870 ℃.

Rapidly cooling the sintered body when the first temperature range is reached may include: when the first temperature range is reached, the sintered body is cooled at a cooling rate of 2 to 3 ℃/s so that the temperature of the sintered body reaches a range of 200 to 350 ℃.

The preparing of the sintered body by sintering the molded body may include: the sintered body is prepared by sintering the molded body at a sintering temperature of 1110 to 1160 ℃ for 25 to 35 minutes.

The preparing of the sintered body by sintering the molded body may include: a sintered body was prepared using a gas of nitrogen mixed with hydrogen at a nitrogen to hydrogen ratio of 8:2-9:1.

The sintered body may have 6.85 to 6.95g/cm ³ The overall density of (a).

According to another aspect of the present disclosure, a slider of a variable oil pump for a vehicle includes: 0.4 to 0.6% of carbon (C), 2.8 to 3.2% of chromium (Cr), 0.45 to 0.55% of molybdenum (Mo), 0.35 to 0.5% of manganese (Mn), 0.1 to 0.25% of sulfur (S), and the balance of iron (Fe) and inevitable impurities, in terms of percentage (%) based on the total composition weight; and tempered martensite as a microstructure.

The content of carbon (C) may be 0.45 to 0.55%.

The sliding member may further include bainite in the core at 5% or less as a microstructure.

The sliding member may have a surface hardness of hv0.3 or more.

According to still another aspect of the present disclosure, a variable oil pump includes: a rotor; a plurality of blades inserted into a plurality of radiation channels formed in the rotor; and a slider configured to change a pumping amount by pressing the vane upon the rotational movement.

Drawings

These and/or other aspects of the present invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 is a diagram showing a slider of a variable oil pump for a vehicle;

FIG. 2A is a conceptual diagram illustrating a prealloy in accordance with disclosed embodiments, and FIG. 2B is a conceptual diagram illustrating a mixed powder;

FIGS. 3A and 3B are graphs illustrating temperature changes of a sintering process and a cooling process according to disclosed embodiments; and

fig. 4 is a flowchart illustrating a method of manufacturing a slider of the variable oil pump for a vehicle according to the disclosed embodiment.

Detailed Description

Like reference numerals refer to like elements throughout the specification. Not all elements of the embodiments of the present disclosure will be described, and descriptions of contents that are known in the art or overlap each other in the embodiments will be omitted.

It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof, unless the context clearly dictates otherwise.

As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings and tables.

Fig. 1 is a diagram showing a slider of a variable oil pump for a vehicle.

Referring to fig. 1, the variable oil pump includes: a rotor 1 rotating together with the rotation shaft to transmit power; a plurality of blades 10 inserted into a plurality of radiation passages formed in the rotor 1 and moving in a radial direction; a slider 20 that changes a pumping amount by pressing the vane 10 upon a rotational movement; and a housing 5.

The sliding member according to the disclosed embodiment may be manufactured by a sinter hardening method. In general, a material for sinter hardening such as a mixed powder is subjected to a mechanical working or a surface treatment of the outer shape of the sinter-hardened material after the sinter-hardening treatment.

Machining is an operation of correcting the dimensions of a product by applying a pressure load of a plastic region to the profile.

The surface treatment operation is an operation for removing burrs (burr) or improving surface quality by applying a pressure load of an elastic zone to the profile, rather than correcting the dimensions. In this case, per unit area (cm) ² ) The forming pressure of (a) may be 6 to 7 tons.

In the case of a complicated shape such as a sliding member, the cooling rate is different for each portion due to the size effect, and therefore, the change in the outer dimension is large due to contraction and expansion caused by the martensite transformation, and machining is required. However, due to the high strength of the sliding member, the load for correcting the shape is high, so that there may occur a problem of damage of the mold or the like. In addition, since the amount of springback is large, the setting effect is not significant, and thus the major dimension is adjusted by the cutting process in some cases. In addition, since the sliding member of the above-described variable oil pump has an asymmetric shape and high dimensional accuracy, it is difficult to control the dimensions by a conventional sinter hardening process.

The disclosed embodiments provide a method of manufacturing a sliding member of a variable oil pump for a vehicle, in which a microstructure having excellent wear resistance is obtained and dimensional change is minimized by an improved sinter hardening method.

First, the sliding member according to the disclosed embodiment uses pre-alloyed powder to increase the dimensional accuracy of the outer shape, thereby omitting the machining process. Fig. 2A is a conceptual diagram illustrating a pre-alloy according to a disclosed embodiment, and fig. 2B is a conceptual diagram illustrating a mixed powder.

The prealloyed powder according to the disclosed embodiments includes, in percent (%) by weight of the total components, 0.45 to 0.55% carbon (C), 2.8 to 3.2% chromium (Cr), 0.45 to 0.55% molybdenum (Mo), 0.35 to 0.5% manganese (Mn), 0.1 to 0.25% sulfur (S), and the balance iron (Fe) and unavoidable impurities.

When the above elements do not reach the respective compositional ranges, a large dimensional change occurs first, and it is difficult to have a hardness value of hv3.0 or more. In addition, when the above elements are out of the composition range, formability is deteriorated, and thus the overall density does not reach a target level, for example, 6.9.

The prealloyed powder has a more uniform alloy composition than that of conventional sinter-hardened powders and therefore has little dimensional change during rapid cooling. Referring to FIG. 2A, it can be seen that the prealloyed powder according to the disclosed embodiments has a Cr-Mo composition or a Ni-Mo composition uniformly distributed in the Fe powder.

For example, in the prealloyed powder, the content of the Cr — Mo component is measured in a molten state. According to the present disclosure, the content of the Cr component in the molten state is in the range of 2.95 to 3.05%, and the content of the Cr component in the powder state is in the range of 2.8 to 3.2%, with a deviation of 5%.

However, referring to fig. 2B, the mixed powder has Cr, mo, ni, cu, and C components mixed or diffused into some Fe matrix adjacent to the surface of the iron powder, wherein alloy components (Ni, cu, mo, cr, etc.) are difficult to uniformly diffuse in the Fe matrix even after sintering, thereby forming a mixed structure upon slow cooling. If the sintering temperature is kept above 1200 c for a long time, the alloy components can be uniformly diffused into the Fe powder, but shrinkage or expansion according to the type of alloy occurs, which causes difficulty in dimensional control.

The pre-alloyed powder according to the disclosed embodiments has the alloying elements fully diffused before sintering and forms a single structure upon slow cooling, so the dimensional change after sintering is very small.

On the other hand, the higher the bulk density, the larger the dimensional change before and after sintering, and therefore, in order to stably predict the dimensional change, the bulk density of the molded body or sintered body is limited to 6.85 to 6.95g/cm ³ . Here, the bulk density refers to a density value measured without cutting a part.

In the method of manufacturing the sliding member of the variable oil pump for a vehicle according to the disclosed embodiment, the pre-alloyed powder having the above-described composition range is molded into a sliding member shape, and the sliding member molded body is sintered to form a sliding member sintered body.

Fig. 3A and 3B are graphs illustrating temperature changes of a sintering process and a cooling process according to the disclosed embodiments.

As described above, pre-alloyed powders may be used to improve dimensional accuracy, and sinter hardening methods according to disclosed embodiments may be used to further improve dimensional accuracy.

Referring to fig. 3A, a compact formed from prealloyed powder is sintered in a sintering furnace set to a temperature range of 1110 to 1160 ℃, according to the disclosed embodiments. According to an exemplary embodiment, sintering is performed at a temperature of about 1120 ℃ for 25 to 35 minutes, and a gas in which nitrogen is mixed with hydrogen at a nitrogen-to-hydrogen ratio of 8:2-9:1 is used as a sintering gas.

According to the disclosed example 50, the above sintering process is not immediately followed by rapid cooling, but the sintered body is slowly cooled by furnace cooling until the temperature of the sintered body reaches the temperature range of 830 to 870 ℃, unlike the conventional sinter hardening method according to comparative example 40. When the temperature of the sintered body reaches a temperature range of 830 to 870 ℃, the sintered body is cooled to 200 to 350 ℃ (Mf point) at a cooling rate of 2 to 3 ℃/s.

Such slow cooling is performed to further refine the austenite structure that becomes coarse through the sintering process performed at a temperature of about 1120 ℃, and blowing (blowing) is used to reduce the cooling time. Since the cooling capacity in the cooling converting section is limited, when cooling is started at a lower temperature than in the comparative example, the cooling time is shortened, which causes the surface of the sintered body to be rapidly cooled to a level close to the Mf temperature, whereby the dimensional change is reduced to within 0.1%, improving the dimensional accuracy.

In general, there is a temperature jump section between the Ms temperature and the Mf temperature at the time of cooling, and therefore the time after the Ms temperature passing through the Mf temperature section depends on the cooling start temperature. As in the disclosed example 50, when cooling is started at a temperature lowered by about 200 to 250 ℃ relative to the sintering temperature, martensite transformation easily occurs and the formation of retained austenite is suppressed.

On the other hand, after the Mf temperature, the cooling rate is decreased due to the latent heat of the core portion of the sintered body, so that the time during which the rapidly cooled structure of the surface portion of the sintered body is exposed in the interval of 150 to 250 ℃ is increased to one hour or more, whereby the tempering effect can be obtained. Thus, a separate tempering process may be omitted or reduced. Similar to the machining process, tempering is not an essential process. The tempering may be performed at a temperature range of 180 to 220 c for one hour, as required.

On the other hand, when the cooling rate immediately after sintering is 2.4 to 3.0 ℃/s, a tempered martensite structure is formed on the entire sliding member, and when the cooling rate is 2.0 to 2.4 ℃/s, a tempered martensite structure and a bainite structure of less than 5% are formed in the core portion.

As described above, the sintered body is formed of the pre-alloyed powder, and after sintering, the sintered body is not immediately subjected to the rapid cooling process but to the slow cooling process, and then is subsequently subjected to the rapid cooling process, so that the dimensional accuracy can be improved, and the machining process of the outer shape can be omitted.

The sliding member manufactured through the above-described process can achieve a surface hardness of hv0.3 or more, and more specifically, as shown in table 1 below, a surface hardness of hv0.3 650.

Table 1 below shows data of exemplary examples and comparative examples.

[ Table 1]

Comparative example 1 shows a conventional sinter hardening method in which slow cooling is not performed immediately after sintering, and comparative example 2 has a low bulk density, comparative example 5 has a high bulk density, and other comparative examples have different compositional ranges. When compared with the comparative examples, it can be seen that the comparative examples have a larger change in the outer diameter of the sliding member when cooled at a cooling rate of 2.5 ℃/s than the examples of the present disclosure. When the tolerance of the variation of the outer diameter dimension of the sliding member is within ± 0.03, it is necessary to machine a product which does not meet the outer diameter dimension standard. When the dimensional change rate of the comparative example is converted into the outer diameter size and the standard of the outer diameter size is Φ 65 ± 0.03, the outer diameter size provided by comparative example 1 is 64.948, the outer diameter size provided by comparative example 2 is 64.928, the outer diameter size provided by comparative example 5 is 65.052, and the outer diameter size provided by the exemplary embodiment is 64.987. That is, only the exemplary embodiment has the result of falling within a tolerance range of ± 0.03 with respect to the outer diameter dimension 65, so that the machining process may be omitted.

Fig. 4 is a flowchart illustrating a method of manufacturing a slider of the variable oil pump for a vehicle according to the disclosed embodiment. Next, a manufacturing method of a slider of a variable oil pump for a vehicle according to the disclosed embodiment will be described with reference to fig. 4.

Referring to fig. 4, a forming body (100) is formed using pre-alloyed powder, the forming body (110) is sintered, the sintered body (120) is slowly cooled, and the sintered body (140) is rapidly cooled when the temperature of the sintered body reaches a first temperature range (130).

The prealloyed powder according to the disclosed embodiments may include, in percent (%) by weight of the total components, 0.45 to 0.55% carbon (C), 2.8 to 3.2% chromium (Cr), 0.45 to 0.55% molybdenum (Mo), 0.35 to 0.5% manganese (Mn), 0.1 to 0.25% sulfur (S), and the balance iron (Fe) and unavoidable impurities.

The prealloyed powder has a more uniform alloy composition than that of conventional sinter-hardened powders and therefore has less dimensional change upon rapid cooling. Referring to FIG. 2A, it can be seen that the prealloyed powder according to the disclosed embodiments has a Cr-Mo composition or a Ni-Mo composition uniformly distributed in the Fe powder. The pre-alloyed powder according to the disclosed embodiments has the alloying elements fully diffused even before sintering, and thus forms a single structure upon slow cooling, so that the dimensional change after sintering is very small.

In the method of manufacturing the sliding member of the variable oil pump for a vehicle, the prealloyed powder having the above-described composition ranges is molded into a sliding member shape, and the sliding member molded body is sintered to form a sliding member sintered body.

According to a disclosed embodiment, referring to fig. 3A, a compact formed from pre-alloyed powder is sintered in a sintering furnace set to a temperature range of 1110 to 1160 ℃. According to an exemplary embodiment, sintering is performed at a temperature of about 1120 ℃ for 25 to 35 minutes. As the sintering gas, a gas in which nitrogen and hydrogen are mixed at a nitrogen-hydrogen ratio of 8:2-9:1 was used. In addition to the above mixed gas, hydrogen gas may be used as a sintering gas, and sintering may be performed even in a vacuum state without the sintering gas.

When the above sintering process is completed, the sintered body is slowly cooled by furnace cooling until the temperature of the sintered body reaches a temperature range of 830 to 870 ℃. When the temperature of the sintered body reaches a temperature range of 830 to 870 ℃, the sintered body is cooled to 200 to 350 ℃ (Mf point) at a cooling rate of 2 to 3 ℃/s.

Such slow cooling is performed to further refine the austenite structure that becomes coarse through the sintering process performed at a temperature of about 1120 ℃, and blowing is used to reduce the cooling time. Since the cooling capacity in the cooling converting section is limited, when cooling is started at a lower temperature than in the comparative example, the cooling time is shortened, which causes the surface of the sintered body to be rapidly cooled to a level close to the Mf temperature, whereby dimensional change is reduced to within 0.1%, improving dimensional accuracy.

On the other hand, after the Mf temperature, the cooling rate is reduced due to the latent heat of the core portion of the sintered body, and thus the time during which the rapidly cooled structure of the surface portion of the sintered body is exposed in the interval of 150 to 250 ℃ is increased to one hour or more, so that the tempering effect can be obtained. Thus, a separate tempering process may be omitted or reduced. As described above, the sintered body is formed of the pre-alloyed powder, and after sintering, the sintered body is not immediately subjected to the rapid cooling process but to the slow cooling process, and then is subsequently subjected to the rapid cooling process, so that the dimensional accuracy can be improved, and the machining process of the outer shape can be omitted.

As apparent from the above, the manufacturing method of the sliding member of the variable oil pump for a vehicle can improve wear resistance and external dimensional accuracy, so that a separate machining process for dimensional correction can be omitted.

In addition, the cooling section is shortened, and self-tempering can be performed only by using the latent heat of the self-tempering section.

Although the embodiments of the present disclosure have been described with reference to the accompanying drawings, those skilled in the art will appreciate that other specific modifications can be easily made without departing from the technical idea or essential features of the present disclosure. The foregoing embodiments are therefore to be considered in all respects illustrative rather than restrictive.

Claims

1. A method of manufacturing a slider of a variable oil pump for a vehicle, the method comprising:

preparing a compact of a sliding member of the variable oil pump using a prealloyed powder including, in percent by weight, that is,% of the total components, 0.45 to 0.55% of carbon (C), 2.8 to 3.2% of chromium (Cr), 0.45 to 0.55% of molybdenum (Mo), 0.35 to 0.5% of manganese (Mn), 0.1 to 0.25% of sulfur (S), and the balance iron (Fe) and inevitable impurities;

preparing a sintered body by sintering the molded body;

slowly cooling the sintered body by furnace cooling to a temperature of the sintered body in a first temperature range of 830 to 870 ℃; and

rapidly cooling the sintered body at a cooling rate of 2 to 3 ℃/s when the first temperature range is reached, so that the temperature of the sintered body reaches a range of 200 to 350 ℃,

wherein the sintered body has 6.85 to 6.95g/cm ³ The overall density of (a).

2. The method of claim 1, wherein preparing the sintered body comprises preparing the sintered body by sintering the shaped body at a sintering temperature of 1110 to 1160 ℃ for 25 to 35 minutes.

3. The method of claim 1, wherein preparing the sintered body comprises: the sintered body was prepared using a gas of nitrogen mixed with hydrogen at a nitrogen to hydrogen ratio of 8:2-9:1.

4. A slider of a variable oil pump for a vehicle, the slider comprising:

0.4 to 0.6% of carbon (C), 2.8 to 3.2% of chromium (Cr), 0.45 to 0.55% of molybdenum (Mo), 0.35 to 0.5% of manganese (Mn), 0.1 to 0.25% of sulfur (S), and the balance iron (Fe) and inevitable impurities, in% by weight of the total composition; and

as a tempered martensite of a microstructure, a tempered martensite,

wherein the sliding member is manufactured by slowly cooling a sintered body prepared by sintering a molded body and then rapidly cooling the sintered body,

the slow cooling includes furnace cooling the sintered body to a first temperature range of 830 to 870 ℃,

the rapid cooling includes cooling the sintered body at a cooling rate of 2 to 3 ℃/s so that the temperature of the sintered body reaches a range of 200 to 350 ℃ when the first temperature range is reached, and

the sintered body has 6.85 to 6.95g/cm ³ The overall density of (a).

5. The sliding member according to claim 4, wherein the content of carbon (C) is 0.45 to 0.55%.

6. The sliding member according to claim 4, further comprising bainite in the core at 5% or less as a microstructure.

7. The sliding member according to claim 4, wherein the sliding member has a surface hardness of Hv0.3 or more.

8. A variable oil pump comprising:

a rotor;

a plurality of blades inserted into a plurality of radiation channels formed in the rotor; and

the slider of claim 4, wherein the slider changes the pumping amount by pressing the vane upon rotational movement.